Quadrupolar mixed modes with near-degeneracy effects in an early red giant and their role in constraining stellar parameters

by Dr Meenakshi Gaira (DAA, TIFR)

Tuesday 23 Jun 2026, 11:00 → 12:00 Asia/Kolkata

AG-69

Asteroseismology is the study of stellar oscillations to probe the internal structure and dynamics of stars. Evolved solar-like stars exhibit mixed modes that result from the coupling between pressure($p$)  and  gravity($g$) modes. Dipolar mixed modes have proven to be extremely useful for constraining the internal structure and dynamics of evolved stars. In this talk, I will discuss quadrupolar mixed modes, which are often modeled as pure pressure modes in asteroseismic analyses, since the coupling between quadrupolar $p$ and $g$ modes is roughly an order of magnitude weaker than that for dipolar modes. However, their rotational splittings are substantially affected by near-degeneracy effects, which arise when the frequency spacing between successive mixed modes is comparable to or smaller than the rotational splittings. Correct characterization of rotational multiplets of quadrupolar mixed modes is important for putting constraints on latitudinal differential rotation and for investigating angular momentum transport mechanisms in evolved solar-like stars.

I will present our detailed analysis of a young red giant whose quadrupolar rotational multiplets show substantial asymmetry due to near-degeneracy effects. Using asymptotic theory and an implicit approach to account for near-degeneracy effects, we performed a global fit of the quadrupolar mixed modes to measure their coupling strength and characterize their rotational splittings. We then carried out grid-based stellar modeling and assessed how incorporating the quadrupolar mixed-mode frequencies as constraints influences the uncertainties in inferred stellar parameters.